The striking similarity between Berlin's (Pedro Alonso) ex-wife Tatiana (Diana Gómez) and police investigator Alice Sierra (Najwa Nimri) in Netflix's crime caper series Money Heist has led fans to theorize that they're actually the same person. Both characters were introduced in Money Heist season 3: Sierra as the main police strategist during the Bank of Spain heist, and Tatiana appearing in flashbacks to Berlin's romance with her.
Beyond the two actresses having very similar faces, Tatiana and Alicia also both have red hair that's worn in a style with bangs, further highlighting the resemblance. However, there are other reasons to be on the lookout for surprise connections between characters in Money Heist. At the end of season 2 it was revealed that the Professor (Álvaro Morte) and Berlin are actually brothers, so it wouldn't be surprising if there was another big reveal during the Bank of Spain heist.
Though Tatiana is only one of Berlin's five ex-wives, she had a considerable amount of build-up that has yet to be fully paid off. Berlin first introduces the Professor to his new love by showing him a photograph of Tatiana. Then, in Money Heist season 3, episode 6, the two are properly introduced in a scene where Tatiana approaches the Professor and removes her hat and sunglasses, resulting (perhaps accidentally) in a rather dramatic reveal of her having a close resemblance to Alicia. Later, after Berlin and Tatiana were celebrating their wedding, the Professor scolded his brother for marrying someone so young and in love, knowing that his disease would kill them early in their marriage. As it turns out, though, Berlin outlived the marriage; in Money Heist season 1 he revealed that he had been married five times, and divorced five times.
Money Heist certainly seemed to be communicating that Tatiana was an important character, and the Professor expressed concern that - in knowing the details of the heist plan - she might be a liability. But while it felt like the show was setting Tatiana up to return in the modern day storyline, she has yet to appear outside of flashbacks. This is what led to fans theorizing that perhaps they had already met her: that Alicia was actually a slightly older Tatiana. There's even been speculation that Alicia is really pregnant with Berlin's baby (though for that to be true, Berlin would need to have secretly survived being gunned down at the end of Money Heist season 2).
Of course, there are a number of issues with this fan theory, starting with the fact that the characters are played by two different actresses and the flashbacks are only separated from the modern storyline by a few years. There's also the fact that the Professor, who met Tatiana on numerous occasions and was even at her wedding to Berlin, doesn't appear to recognize Alicia. He would obviously be alarmed to discover that the lead negotiator happened to be a person who was once married to his brother and knew what the plan for the heist was. Similarly, Alicia has by all accounts been keeping pace with the heist crew by outwitting them rather than demonstrating inside knowledge of the plan.
Money Heist season 4 ended with the Bank of Spain heist still in progress, so it's possible that we'll see Tatiana return in the present day in season 5, to pay off the build-up in the flashbacks. But given that this is a show where a crew of bank robbers dropped a shower of notes from a blimp just to create a diversion, the possibility of Tatiana marrying Berlin as part of an undercover police operation and later getting cosmetic surgery to change her face can't be completely written off either.